Linear Algebra/Glossary

A

adjugate 

Also called classical adjoint. The matrix adj A formed from a square matrix A by replacing the (i, j)-entry of A by the (i, j)-cofactor, for all i and j, and then transposing the resulting matrix.

affine transformation 

A mapping $T:\mathbb{R}^n\rightarrow\mathbb{R}^m$ of the form T(x) = Ax + b, with A an $m \times n$ matrix and b in $\mathbb{R}^m$.

algebraic multiplicity 

The multiplicity of an eigenvalue as a root of the characteristic equation.

angle 

Between nonzero vectors u and v in $\mathbb{R}^2$ and $\mathbb{R}^3$. The angle $\vartheta$ between the two directed line segments from the origin to the points u and v. Related to the scalar product by $u \bullet v=\left \Vert u \right \Vert \left \Vert v \right \Vert \cos \vartheta$

C

coefficients 

A constant by which a variable are multiplied, fx. $2\,$ are a coefficient in the following equation $2x=4\,$.

consistent linear system 

A linear system with at least one solution.

E

equivalent linear systems 

Linear systems with the same solution set.

echelon form 

Also called row echelon form. An echelon matrix that is row equaivalent to the given matrix.

echelon matrix 

Also called row echelon matrix. A rectangular matrix that has three properties: (1) All nonzero rows are above any row of all zeros. (2) Each leading entry of a row is in a column to the right of the leading entry of the row above it. (3) All entries in a column below a leading entry are zero.

I

inconsistent linear system 

A linear system with no solution.

L

linear equation 

An equation that can be written in the form $a_1x_1+a_2x_2+...+a_nx_n=b\,$, where b and the coefficients $a_1,...,a_n\,$ are real or complex numbers.

linear system 

A collection of one or more linear equations involving the same variables, fx. $x_1,...,x_n\,$.

R

reduced echelon form 

Also called reduced row echelon form. A reduced echelon matrix that is row equivalent to a given matrix.

reduced echelon matrix 

A rectangular matrix in echelon form that has these additional properties: The leading entry in each nonzero row is 1, and each leading 1 is the only nonzero entry in its column.

reduced row echelon form 

See reduced echelon form.

row echelon form 

See echelon form.

row echelon matrix 

See echelon matrix.

S

solution 

A list $\left(s_1,s_2,...,s_n\right)\,$ of numbers that makes each equation in system a true statement when the values $s_1,...,s_n\,$ are substituted for $x_1,...,x_n\,$ respectively.

solution set 

The set of all possible solutions of a linear system. The solution set is empty when the linear system is inconsistent.

system of linear equations 

Also called a linear system, is a collection of one or more linear equations involving the same set of variables, fx. $x_1,...,x_n\,$.